This invention relates to a method of controlling the tension of a strip within a furnace, and more particularly, to such a method of controlling the tension profile of a strip developed within a heating furnace forming a process line including a multitude of carrier rollers for carrying the strip.
A conventional tension control apparatus for carrying out a method of control of the type referred to has comprised a tension controlled strip carried within a furnace by means of multitude of conveying rollers disposed in a plurality of sections into which the furnace is divided. In each section, the conveying rollers are driven by respective electric motors energized by a common electric source connected to a speed regulator. A tension meter is also disposed at an outlet of each section to sense an outlet tension of the strip and to produce an actual outlet tension signal. The actual outlet tension signal is subtracted from a reference tension signal which is output fron a reference tension generator disposed in the associated section. A deviation tension signal corresponding to the difference between the reference tension signal and the actual tension signal is applied to the associated speed regulator along with a common reference speed signal for the conveying rollers.
The speed regulators included in the respective control loops are responsive to the associated deviation tension signals and the reference speed signal applied thereto to change the speeds of the conveying rollers about a reference magnitude thereof so as to vary the tension of the strip carried by the conveying rollers until the actual tension signals sensed by the respective tension meters are respectively equal to the reference tension signals from the associated reference tension generators.
However, conventional tension control apparatus, such as those described above, have been disadvantageous in that: (1) in order to determine a tension profile developed in the respective sections as a whole, it is necessary to manually adjust the reference tension generators separately on all such occasions and only by relying on the rule of trial and error, (2) it is difficult to adjust the reference tension generators because a roller driving system disposed in the furnace does not include pinch rollers or the like and exerts only a weak restraint on the strip and because complicated conditions are imposed on the determination of the reference tension signals, and (3) the strip may be damaged due to slips of the rollers relative to the strip because of the fact that the rate of change in tension profile in the longitudinal direction of the furnace can not be controlled.
Accordingly, it is an object of the present invention to provide a new and improved control method of easily controlling the tension of a strip moved within a furnace without an excessive control force occurring and with a change in tension as a whole maintained so as to be sufficiently small.